This invention generally relates to vehicle security systems and, more particularly, to a low power transmitter for remote access to the vehicle security system.
A variety of vehicle security systems are available today. Some are installed by the manufacturer while others are available on an after-market basis. In most vehicle security systems, a remote access feature is provided through a key fob. The key fob typically includes one or more buttons that can be pressed to activate or access the vehicle security system. For example, a button can be pressed to unlock the vehicle doors from some distance away from the vehicle.
In some markets and areas, it is becoming increasingly important to customize vehicle security systems to fit within certain operating parameters. For example, in Japan, the signals that are transmitted by a remote transmitter must be of a much lower power level than that typically used in the United States. Current attempts to address this situation utilize special integrated circuitry within the key fob transmitter. Alternatively, metal shielding has been introduced to isolate the various components within the key fob, which permits lower power signal operation. Neither of these solutions is satisfactory because they both introduce undesirable cost into the system.
There is another difficulty in designing a system that operates at a low power level. In conventional systems, the transmitter includes an oscillator and an antenna. The antenna is typically coupled with the collector of the oscillator and, therefore, is a load on the oscillator. Since the antenna is influenced by outside factors, the oscillator must be robust in the conventional arrangements. An oscillator that is more robust carries with it the undesirable drawback of yielding higher harmonic levels if low power levels are used. Another significant problem with conventional designs is that lowering power within the circuitry compromises the performance of the oscillator and, therefore, the output signal from the key fob.
There is a need for a transmitter for use with a vehicle security system, for example, that allows for low power operation without compromising oscillator performance. This is a challenge that has not been met prior to this invention.